1. Field of the Invention
The present invention relates to a wireless LAN technique, and in particular to an effective technique applicable to a wireless terminal, wireless base station (i.e., an access point), management apparatus and the related control method, et cetera.
2. Description of the Related Art
In recent years, the wireless LAN has become increasingly popularized eliminating the need for a cable, in addition to the conventional fixed line LAN (local area network), as a telecommunication medium for information systems in the enterprise. A public wireless LAN service has also emerged allowing the Internet connections in a neighboring area of the location where telecommunication equipment, so called wireless base stations (i.e., access points), are installed in public spaces such as train stations, airports, hotels and coffee shops.
Enterprise and public wireless LAN systems provide respective telecommunication services over a wide range by installing a plurality of access points, because radio waves from a single access point have a limited usage range. And such a wireless LAN system is based on a common SSID (service set ID), which identifies the wireless LAN network, for all access points so as to enable a user to use all the access points of the wireless LAN system by registering one SSID in the wireless terminal.
Conventionally, a wireless terminal connects to an access point with the highest radio wave intensity from among the access points detected by a scanning, et cetera, when utilizing the above described wireless LAN system.
When using a wireless LAN system in a place where many users gather, such as a conference room, however, the connections concentrate on a single access point since the radio wave conditions received by wireless terminals are approximately the same, thus creating a problem of degrading the telecommunication quality received by all the wireless terminals connected to the access point.
As a countermeasure to the above described problem, a patent document 1 has disclosed a technique whereby a management terminal is installed for managing all the access points in a wireless LAN system so that the management terminal determines an access point for a wireless terminal to connect to. That is, the wireless terminal sends out a connection request signal to all the recognized access points when using a wireless LAN system so that the received access points transmit the connection request signal including their respective radio wave levels to a management terminal. The management terminal then determines an access point as a connection destination for the wireless terminal based on the number of wireless terminals being connected to each access point and the information about the message contained in the transmitted connection request, thereby avoiding concentrated connection to the access point.
The technique disclosed by the patent document 1, however, is faced with a technical problem of wasting wireless resources unnecessarily since each wireless terminal transmits a connection request signal to all the recognized access points.
There is also another technical problem that the management terminal cannot judge how many access points are recognized by the wireless terminal which has transmitted the connection request signal or to which access points the wireless terminal has transmitted the connection request signal, because the connection request signals transmitted to the respective access points are mutually independent, and therefore it takes time to determine an access point as the connection destination.
Meanwhile, a currently marketed wireless LAN switch has the function of distributing connections to one access point, as disclosed in a patent document 2. This function is for refusing a connection of a wireless terminal to a load concentrated access point and making the wireless terminal try to connect to another access point, thereby distributing a load on the access point. There is, however, a technical problem that a wireless terminal takes time to select a connectable access point.
Another patent document 3 has disclosed a technique for furnishing each access point with a wireless terminal certification-use database registering wireless terminal apparatuses which are permitted to join a wireless network and with a wireless terminal management-use database registering wireless terminal apparatuses which are currently under management and for furnishing wireless terminals with a management side recognition-use database, thereby accomplishing a retransmission from an access point to a wireless terminal on the MAC level and a restriction on a wireless terminal apparatus in joining each access point.
The case of the technique noted in the patent document 3, however, is configured to such that an access point has the above described various databases and therefore is faced with the technical problem that the work of installing, adding, moving, et cetera, each access point becomes cumbersome as compared to the case of managing a plurality of base stations integrally by a management apparatus, et cetera.
[Patent document 1] laid-open Japanese patent application publication No. 10-41969
[Patent document 2] laid-open Japanese patent application publication No. 2005-117357
[Patent document 3] laid-open Japanese patent application publication No. 06-261043